In Westchester County, a television advertisement accused a Democrat running for the State Senate of using campaign money to treat himself to fancy dinners. In Rochester, a commercial branded a Republican candidate as anti-women. And in Queens, a mailer attacked a Democratic incumbent for providing taxpayer money to a nonprofit organization that facilitates parrot adoptions.

The searing advertisements have one thing in common: they were financed by independent groups, not political campaigns. As both parties battle for control of the State Senate, the most forceful attack advertisements have been concentrated in a handful of races that will determine who controls the chamber — and, increasingly, they are being drawn up by outside groups, including some not even in New York State.

There will be 213 seats in the Legislature next year, and all of them are on the ballot Nov. 6. But much of the independent spending has been focused on just three Senate races — in Queens, Westchester County and Rochester — that are critical to determining the balance of power. Outside groups are on track to funnel at least $2 million into those three races — a large sum of money in legislative campaigns, where hundreds of votes can separate the candidates.

The spending by outside groups comes on top of a prodigious amount of cash raised by lawmakers. Senate candidates, party organizations and related campaign committees have nearly $24 million on hand, more than three-quarters of which was raised by Republicans, according to the New York Public Interest Research Group.

The surge of money into Senate races reflects the intense desire by Republicans and Democrats alike to win control of the chamber, in which Republicans hold a 33-to-29 majority. Polls and pundits have suggested Republicans are likely to retain control, but Democrats have said they are hoping high turnout driven by the presidential race will lead to some surprise victories.

The advertisements financed by independent groups are infuriating candidates and government reformers alike.

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This ad, critical of the Democrat Ted O'Brien of the Rochester area, and similar ones were made by groups not affiliated with a political party. Under current state laws, such organizations can remain mysterious.

“It gives the race a negative vibe, and it’s unfortunate,” said Alexander Blenkinsopp, a graduate student and member of Community Board 9 in Queens, who recently posted on Twitter a collection of mail he had received attacking a Democratic incumbent, Senator Joseph P. Addabbo Jr. “It seems to me like the people in the district should be the ones who have a say over what their representative is going to do in Albany, and when you have all of these well-funded, shadowy outside institutions getting involved in this local race, it feels like someone’s trying to take it out of our hands.”

The independent spending also highlights New York State’s notoriously lax campaign-finance laws, which in many instances do not require groups that run attack ads to reveal anything about themselves. The average voter would be hard-pressed to identify who is behind many of the advertisements and mailers financed by third-party groups.

For instance, a commercial that attacks the Republican candidate in the Rochester Senate race, Assemblyman Sean T. Hanna, discloses only that it was paid for by an entity called the “VOTE/COPE Committee.” A viewer could be forgiven for not recognizing that entity as the political arm of the statewide teachers’ union, New York State United Teachers: the advertisement, which criticizes Mr. Hanna for his positions on issues like hydraulic fracturing, women’s health issues and gun control, never mentions education.

“It’s critically important for the people of New York, a state that’s so large and so diverse, that they have balance in their government,” said Matthew Walter, the committee’s political director, who is a former executive director of the New York State Republican Party.

Perhaps the most mysterious advertisements have come from a group based outside Richmond, Va., which calls itself Common Sense and has produced a blizzard of mailers attacking Democratic candidates in the three Senate districts.

One displayed a missing poster bearing the face of Assemblyman George S. Latimer, the Democrat running for the Senate seat in Westchester, and criticized him for skipping votes in the Legislature; others accusing Mr. O’Brien of hypocrisy featured an image of a pair of flip-flops in one case and a chameleon in another. (Both the flip-flops and the chameleon were rainbow-colored, which Democrats suggested was meant to associate Mr. O’Brien with the gay-rights movement; the senator he is seeking to succeed, James S. Alesi, a Republican who did not seek re-election, previously opposed same-sex marriage but voted for its legalization last year.)

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An ad critical of Assemblyman George Latimer, a Democrat of Westchester County, that was produced by Common Sense, a group based outside Richmond, Va.

On its Web site, Common Sense says it is inspired by the principles of Thomas Paine, and in a filing with the Internal Revenue Service last year, it described its mission as “advocating smaller government and responsible tax and budget policies.” Filings with the I.R.S. and the Commonwealth of Virginia show that the organization, founded in 2010, is directed by Christopher J. LaCivita, a Republican strategist in Virginia who advised Swift Boat Veterans for Truth.

Records also show that, as recently as last year, Common Sense was also led by a Virginia political consultant named Kevin A. Wright, who has ties to Republicans in New York. Campaign-finance filings show that the New York Senate Republicans paid Mr. Wright more than $40,000 in 2007 and 2008 for research. And in this election cycle, his firm, Old Dominion Research Group, has been paid more than $14,000 by Senator Thomas W. Libous of Binghamton, who leads the Senate Republicans’ campaign committee; the Republican Party in Broome County, Mr. Libous’s home county; and Senator Mark J. Grisanti, a Buffalo Republican.

Mr. LaCivita declined to comment. Mr. Wright, in a brief telephone interview, declined to discuss the origins of Common Sense, but said that he had not worked for the group since the 2010 elections and that his involvement had nothing to do with his earlier work for the Senate Republicans. “There’s no connection whatsoever,” Mr. Wright said. “Absolutely none.” And Scott Reif, a spokesman for the Senate Republicans, said: “We don’t know anything about them. Period.”

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But Senator Michael N. Gianaris, a Queens Democrat who is leading his party’s campaign efforts, questioned why political consultants in Virginia were so acutely interested in three state legislative races in New York.

“The messaging and the targets of this group are so much in line with what the Senate Republicans are doing that it doesn’t pass the straight-face test,” said Mr. Gianaris, who accused the Senate Republicans of “making a mockery of our campaign-finance laws.”

A landmark ethics overhaul enacted last year directed the State Board of Elections to develop rules for the disclosure of outside spending in state elections. But the board’s new regulations, which were approved in September and take effect next week, require disclosure only in the case of advertisements that explicitly advocate the election or defeat of a candidate.

“You don’t need to hire a team of campaign-finance lawyers to figure out how to evade disclosure under the Board of Elections regulation,” said Adam Skaggs, a senior counsel for the Democracy Program at the Brennan Center for Justice at New York University School of Law. “It’s as simple as pie. And all you do is leave out the ‘vote for’ or ‘vote against.’ ”

A version of this article appears in print on October 17, 2012, on Page A25 of the New York edition with the headline: Attack Ads, by Outside Groups With Murky Ties, Shape 3 New York Senate Races. Order Reprints|Today's Paper|Subscribe